1. Field of the Invention
The present invention relates to a device that can appropriately check parts of an optical disk such as a CD or a DVD, which were processed for copyright protection purposes during the manufacturing of the optical disk.
2. Background Art
To meet the needs of the market for large amounts of low-priced digital works, manufacturers of optical disks run round-the-clock manufacturing for greater output. A manufacturing procedure of an optical disk is roughly made up of the following steps: (1) substrate formation; (2) reflective film application; (3) protective film coating; (4) substrate bonding; and (5) label printing. In recent years, a processing step that is intended for copyright protection is often added to this manufacturing procedure. The processing step writes special pits, which cannot be made by commercially available recording devices, onto an optical disk on which a digital work is recorded. The special pits serve as pits for certifying the authenticity of the optical disk (certification pits). With the provision of such certification pits, a reproduction device can distinguish original optical disks that record authentic digital works, from optical disks that record copies of the digital works. As one example, a pit having a length of 15T or more (T denotes a channel bit period) is used as a certification pit.
When manufacturing an optical disk, a defect which the reproduction device could confuse with a certification pit may naturally occur. Such a naturally-occurring defect causes the reproduction device to commit false recognition. Which is to say, the reproduction device may judge the optical disk as authentic at some time, but judge the same optical disk as not authentic at other times. Such false recognition can even lead to a quality dispute in the market. Therefore, optical disks should not be shipped without removing such naturally-occurring defects that are confusable with certification pits.
This problem can be overcome by introducing a step for checking the presence or absence of naturally-occurring defects. However, only a limited time can be spent for such a step. In manufacturing of optical disks that require mass production, if too much time is spent on the check, the production schedule would not be met.